DREDGE_135_LH.JPG The Army Corps of Engineers finished its sand movement recently; the city is doing its own annual work on the Great Highway, trucking sand piled up on the norther stretch by the promenade down to the southern stretch by Sloat Ave. at Ocean Beach. SAN FRANCISCO 6/7/05 LIZ HAFALIA
San Francisco Chronicle

Photo: LIZ HAFALIA

DREDGE_135_LH.JPG The Army Corps of Engineers finished its sand...

SAN FRANCISCO / New tack to hold back Ocean Beach erosion / 300,000-ton gift from dredge could curb erosion

San Francisco has waged a battle against the sea at Ocean Beach for more than a century, in recent times spending as much as $400,000 a year to pad the southern stretch of beach with sand that gets scoured away by hungry waves.

But the Army Corps of Engineers is testing a possible solution to the beach erosion that combines cost-effectiveness with environmental savvy, simply by using sand.

Each year, the corps dredges sandy deposits out of the shipping channel outside the Golden Gate. Usually, the dredging ship hauls the sand several miles out to sea and dumps it.

But in the past month, the dredge instead deposited the sand just beyond the breaking waves between Sloat Boulevard and Fort Funston -- startling beachgoers who thought the ship was foundering in the shallow water. Based on recent surveys by the U.S. Geological Survey, the corps believes the currents will move the 300,000 cubic yards of sand into the surf zone, where it could form sandbars and widen the badly eroded beach.

If it succeeds, this approach would be the "least invasive, least expensive and most sustainable" erosion solution, said Peter Mull, a civil engineer for the corps who is heading up the project -- and who surfs frequently at Ocean Beach.

The pilot project, part of the search for a long-term erosion solution at Ocean Beach, has drawn rare praise for the corps from the Sierra Club.

"This really represents a positive direction change," said Mark Massara, director of Sierra Club's coastal programs. "The genius of this ... is the recognition that this sand that we're just throwing into the ocean is a valuable resource and we ought to find ways to utilize that sand that reduce our reliance on coastal armoring."

Ocean Beach is littered with the evidence of the city's struggle to maintain it. A wall of boulders shores up a section of bluff near Sloat, but some rocks have tumbled onto the beach over the years.

On top of the bluff, people used to be able to walk along an access path at the edge of a parking lot along the Great Highway. As the waves wore away at the beach, the path vanished and the lot began to crumble. So the National Park Service, which oversees the area, sheared off the edges of the parking lot.

The natural shoreline used to be several hundred feet inland, but development during the 1800s and early 1900s pushed the coast westward with fill and debris. Sections of the bluff face today are lined with concrete and brick rubble, and even the occasional headstone from an old cemetery.

Frank Filice, manager for capital planning for the city Department of Public Works, said erosion has been a problem "ever since we drew a line in the sand and said, 'This is going to be the city's urban edge.' "

On the edge of that line are the Great Highway, a storm-water treatment plant and a 4.5-mile pipeline that carries the treated water out to sea -- all valuable assets that the city wants to protect.

A series of storms that scoured the beach beginning in the mid-1990s led the city to install the boulder barrier along one section of the Great Highway in 1997. Over the next three years, the city paid $1.3 million to build emergency detour lanes and cushion the beach with thousands of tons of sand.

Then the city tried a different tack: closing the highway annually to dig out sand that piles up along the northern promenade and trucking it to the eroded area. Crews are out doing that work this week, but the amount they will move is dwarfed by what the corps took from the shipping channel.

The corps, the National Park Service and the city face a juggling act: protecting the beach, preserving the highway that 9,000 cars use each day, and providing access for the people who use Ocean Beach.

"What we don't want is to have resolved this problem and watch three or four other problems crop up," Filice said. "We don't want to put stitches in it if a Band-Aid will work."

The U.S. Geological Survey will monitor the dredged sand's movement, and other studies are planned for the next three to four years to help officials decide whether to relinquish Ocean Beach to the sea or try something else, such as building new sand dunes or a breakwater or artificial reef.

Mull, for one, hopes that sand is the answer.

"I have a really good, gut feeling that this is going to work in the long term," he said.